Re: [PATCH RFC] sched/fair: let cpu's cfs_rq to reflect task migration

[Dietmar Eggemann]

Hi  Vincent,

On 04/07/2016 02:04 PM, Vincent Guittot wrote:
> Hi Dietmar,
>
> On 6 April 2016 at 20:53, Dietmar Eggemann <dietmar.eggemann@xxxxxxx> wrote:
> > On 06/04/16 09:37, Morten Rasmussen wrote:
> > > On Tue, Apr 05, 2016 at 06:00:40PM +0100, Dietmar Eggemann wrote:

[...]

> > @@ -2910,8 +2920,13 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> >          if (!entity_is_task(se))
> >                  return;
> >
> > -       rq_of(cfs_rq)->cfs.avg.util_avg += se->avg.util_avg;
> > -       rq_of(cfs_rq)->cfs.avg.util_sum += se->avg.util_sum;
> > +       if (&rq_of(cfs_rq)->cfs == cfs_rq) {
> > +               rq_of(cfs_rq)->cfs.avg.util_avg += se->avg.util_avg;
> > +               rq_of(cfs_rq)->cfs.avg.util_sum += se->avg.util_sum;
> > +       } else {
> > +               rq_of(cfs_rq)->cfs.added_util_avg = se->avg.util_avg;
> > +               rq_of(cfs_rq)->cfs.added_util_sum = se->avg.util_sum;
> > +       }
> >   }
>
> Don't you also need similar thing for the detach ?

Maybe? I ran workloads in tg's and checked last_update_time of cfs_rq
and &rq_of(cfs_rq)->cfs and they always were in sync. That's obviously
only the call-stack 'task_move_group_fair() -> detach_task_cfs_rq() ->
detach_entity_load_avg()' and not the one starting from
switched_from_fair().

[...]

> > But attach_entity_load_avg() is not only called in enqueue_entity_load_avg() for migrated
> > tasks but also in attach_task_cfs_rq() which is called from switched_to_fair() and
> > task_move_group_fair() where we can't assume that after the enqueue_entity_load_avg() a
> > call to update_cfs_rq_load_avg() follows like in
> >
> > enqueue_task_fair():
> >
> >      for_each_sched_entity(se)
> >          enqueue_entity()
> >              enqueue_entity_load_avg()
> >                      update_cfs_rq_load_avg(now, cfs_rq)
> >                      if (migrated) attach_entity_load_avg()
> >
> >      for_each_sched_entity(se)
> >          update_load_avg()
> >              update_cfs_rq_load_avg(now, cfs_rq)
> >
> >
> > Not sure if we can just update the root cfs_rq to se->avg.last_update_time before we add
> > se->avg.util_[avg/sum] to rq_of(cfs_rq)->cfs.avg.util_[avg/sum] in attach_entity_load_avg()?
> >
> > cfs_rq throttling has to be considered as well ...
>
> IIUC this new proposal, the utilization of a task will be accounted on
> the utilization of the root cfs_rq thanks  to
> tsk->se->cfs_rq->tg->se[cpu]->... down to the root cfs_rq. Then, you
> directly add the utilization of the newly enqueued task in the root
> cfs_rq.

Not sure if you're referring to this, but in __update_load_avg() I
suppress the utilization update for se's w/ !entity_is_task(se) and
cfs_rq's w/ &rq_of(cfs_rq)->cfs != cfs_rq  so preventing the first case.

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